Recently, biometric identification technologies are important subjects of various industries in order to ensure information security. As known, a fingerprint identification technology is one of the widely-used biometric identification technologies.
A fingerprint is a pattern composed of many curvy lines. In the enlarged view, these lines are lumpy because these lines comprise alternate ridges and valleys. A fingerprint feature indicates the distribution of these lumpy lines. Generally, everyone has the unique fingerprint feature. The uniqueness of the fingerprint feature can be used as a basis of recognizing the identity.
Conventionally, the fingerprint identification technology is divided into two types, i.e., a capacitive fingerprint identification technology and an optical fingerprint identification technology. According to the capacitive fingerprint identification technology, a capacitance sensor is used for sensing the charges' change, the temperature difference and the pressure of the finger in order to realize the structure of the fingerprint. The optical fingerprint identification technology directly captures the image of the fingerprint. After a light beam is irradiated on the user's finger to generate brightness contrast between the ridges and the valleys of the fingerprint, the fingerprint image is captured by an image pickup module and the fingerprint image is subsequently processed. Although the capacitive fingerprint identification module is slim and small, the cost of the capacitive fingerprint identification module is higher than the optical fingerprint identification module.
Since the space for storing the image or data of each fingerprint is not very large, the fingerprint identification module is gradually applied to the general mobile electronic device or notebook computer. The capacitive fingerprint identification module or the optical fingerprint identification module is used for acquiring the structure or image of the fingerprint. After the acquired structure or image of the fingerprint is calculated according to an algorithm and compared with the stored files, the user's identity is recognized.
Generally, the optical fingerprint identification module acquires the fingerprint image in a swiping manner or a pressing manner. While the finger is moved on the module in the swiping manner, plural images of the finger are captured. Then, the captured images are stitched as a complete fingerprint image by an application program. In the pressing manner, the module is directly pressed by the user's finger. After a certain time period, the fingerprint image is acquired.
Generally, the swiping-type fingerprint identification module is smaller and cheaper. Consequently, the swiping-type fingerprint identification module is suitably applied to the mobile electronic device. However, if the user's finger is not slid in the specified direction at a constant speed, the recognition result is possibly erroneous. The pressing-type fingerprint identification module provides an easy-to-use operation interface. Moreover, since the pressing-type fingerprint identification module acquires the complete fingerprint image through a one-time pressing action, a larger sensitive area is required. Since the fingerprint identification module with the larger sensitive area occupies much space of the mobile electronic device, the fabricating cost is higher.
FIG. 1 is a schematic cross-sectional view illustrating an optical press-type fingerprint identical module according to the prior art. As shown in FIG. 1, the fingerprint identical module 1 comprises an image pickup assembly 11, two light sources 121, 122, a light diffusion plate 13 and a press plate 10. When a finger A is placed on a surface 100 of the press plate 10, the press plate 10 can be pressed by the user. The two light sources 121 and 122 emit light beams. Moreover, the press plate 10 and the light diffusion plate 13 are light-transmissible. Consequently, the light beams can be transmitted through the press plate 10 and the light diffusion plate 13 and projected onto the finger A.
After the light beams are introduced into the light diffusion plate 13, the light beams are guided or refracted to the press plate 10 by the light diffusion plate 13. Consequently, an area light pattern is formed on the press plate 10. Moreover, the light diffusion plate 13 comprises an opening 130. After the light beams are irradiated on the finger A (especially the ridges of the fingerprint), the reflected light beams are transmitted through the opening 130. Consequently, the reflected light beams are received and imaged by the image pickup assembly 11.
As mentioned in FIG. 1 and as previously described, the press plate 10 should have a larger sensitive area in order to provide a one-time pressing action. However, because of the larger sensitive area, some drawbacks occur. For example, since the light beams are emitted by the light sources 121 and 122 at various angles, the light beams are not completely and centrally irradiated onto the finger A. That is, portions of the light beams are directly leaked out from the periphery of the press plate 10 that is located beside the finger A. Under this circumstance, the illuminating efficiency of the light source is impaired, and the imaging quality is adversely affected.
Since the optical fingerprint identification module is widely applied to the mobile electronic device, the user can operate the optical fingerprint identification module in an intuitive and simple manner. However, if the optical fingerprint identification module is costly or bulky and the image capturing efficacy is impaired, the competiveness of the optical fingerprint identification module in the market is reduced.
Therefore, there is a need of providing an improved optical fingerprint identification module so as to overcome the drawbacks of the conventional technologies.